In respect of a pipe cutting technique, an orbital pipe cutting device which performs a cutting operation by cutting a fixed pipe little by little at a specified depth while allowing a cutting tool to revolve around the outer periphery of the pipe has been developed along with the gradual increase in the size and weight of the pipe. The orbital pipe cutting device is equipped with both a cutting tool and a beveling tool so that the pipe cutting device can perform beveling as well as cutting
As one example of the orbital cutting/beveling device mentioned above, there is available a device shown in FIGS. 1 and 2 (hereinafter referred to as prior art 1). As shown in FIGS. 1 and 2, the device of prior art 1 includes a main body 10 configured to place and fix a pipe (P) at the center thereof. A rotary body 20 configured to allow the pipe (P) to pass therethrough and rotated by an electric motor 15 is coupled to one side (the front side) of the main body 10. A cutting tool 31 and a beveling tool 32 are mounted to the front side of the rotary body 20 in an opposing relationship (or in a balanced manner). Each time when the rotary body 20 makes one revolution, the cutting tool 31 or the beveling tool 32 can make a vertical motion (toward the center of the pipe) by a predetermined distance. In this case, the cutting tool 31 and the beveling tool 32 are mounted to blocks 40 which are guided so that the blocks 40 can reciprocate toward and away from the center of the pipe (P) along the front surface of the rotary body 20. Each of the blocks 40 is threadedly coupled to a rotation shaft 50. A gear 51 is formed at the upper end of the rotation shaft 50. Each time when an engaging claw 60 protruding from the main body 10 makes contact with the gear 51, the rotation shaft vertically moves each of the blocks 40 at a pitch corresponding to the rotation angle of the gear 51, whereby the cutting tool 31 and the beveling tool 32 mounted to the blocks 40 can move toward the center of the pipe (P)
Prior art 1 is directed to the device in which, each time when the cutting tool 31 and the beveling tool 32 make one revolution around the pipe (P), the cutting tool 31 and the beveling tool 32 cut into the pipe (P) at a specified depth, thereby cutting or beveling the pipe (P). However, this is a limitative technique which cannot arbitrarily control the motion of the cutting tool and the beveling tool. In other words, the device of prior art 1 cannot arbitrarily control the cutting tool and the beveling tool while the rotary body 20 is being moved.
Since the cutting tool and the beveling tool cannot be arbitrarily controlled, it is impossible to change the cutting conditions depending on the size, material and kind of a workpiece. This may lead to a reduction in cutting efficiency. In some cases, it becomes impossible to perform a cutting operation. Moreover, in order to return the cutting tool and the beveling tool to the original positions after the cutting work is finished, the rotary body needs to be reversely rotated, or the work of returning the rotary body to the original position through the use of a separate reverse rotation means needs to be performed. This is cumbersome and onerous.
In the cutting/beveling device of prior art 1, it is difficult to predict the time at which the cutting tool or the beveling tool becomes dull or gets broken during the work. Thus, the burning of the workpiece is frequently generated due to the damage of the cutting tool or the beveling tool. More specifically, when the tool is dull or broken in the cutting/beveling device of prior art 1, the tool repeats an action of continuously moving toward the workpiece along with the rotation of the gear, even though the workpiece is not cut due to the abnormal tool conditions. As a result of repetition of this state, the load acting between the tool and the workpiece increases. This load may result in breakage of the tool as a whole or the workpiece.
In addition, the cutting/beveling device of prior art fails to solve the problem of inability to machine a workpiece in different shapes, the problem of inability to cut a thick pipe having a predetermined thickness or more, the problem of the gear and the engaging claw being broken due to the collision thereof, the problem of the cutting depth being difficult to control, and the problem of the beveling blade being frequently replaced depending on the beveling angle and shape.
The above problems will be described in more detail. The device of prior art 1 is configured to machine a pipe in the work order shown in FIG. 3. That is to say, the cutting tool 31 and the beveling tool 32 are moved into the pipe (P) as illustrated the first view of FIG. 3. If the cutting tool 31 and the beveling tool 32 are moved deeper, the pipe (P) is subjected to cutting and beveling at the same time in the order of the second to fourth views. Accordingly, the machining of the pipe performed by the device of prior art 1 is limited top plate 12 the cutting shown in FIG. 4A and the cutting and one-surface beveling shown in FIG. 4B.
As illustrated in FIG. 5, cutting can be performed only when the length of the cutting tool 31 for cutting the pipe is larger than the thickness (t) of the pipe to be cut. However, if the length (L) of the cutting tool is increased in order to cut a pipe having a thickness of several tens millimeters or more, the cutting tool cannot withstand the force applied during a cutting process and may be easily broken.
As can be seen in FIG. 6, the blade length (lb) of the beveling tool 32 for beveling a cut surface of a pipe (P) may well be larger than the length of a slant surface of a pipe to be cut. However, as can be appreciated in FIG. 7, the blade length (lb) of the beveling tool is significantly larger than the blade length ((lc) of the cutting tool. Thus, the blade of the beveling tool should bear the corresponding load.
The device of prior art 1 is configured to cut a pipe toward the center thereof by a predetermined depth value each time when the cutting tool makes one revolution. It can be noted that the load borne during a cutting process and the load borne during a beveling process, namely the cutting resistance force (P), acts in different ways. In this regard, the cutting resistance force (P) is determined by the specific cutting resistance (Ks), which depends on the material of a workpiece, the cutting width (l) and the machining depth (dp) and may be represented by the following mathematical formula:P=Ks×l×dp 
Therefore, as can be seen in FIG. 7B, when a cutting tip for performing a severing work is used, a pitch may be calculated by predicting the cutting width (l) and the machining depth (dp) while neglecting the specific cutting resistance which depends on the material of a workpiece. During a beveling work, as can be noted in FIG. 7A, the cutting width (l) varies depending on the thickness (t) of a pipe. It is therefore difficult to select a suitable pitch value for a beveling work (namely, a machining depth per one revolution). For that reason, it is impossible to satisfy different work requirements. This makes it difficult to commercialize the device of prior art 1. Thus, a hardship is encountered in designing a mechanism capable of overcoming the problem of frequent breakage of the beveling tool.
Each time when the gear caught by the engaging claw is rotated at a specified angle, the cutting tool and the beveling tool are moved down to cut a pipe at a specified depth. When one tries to cut and bevel a pipe having a thickness of several tens millimeters or more, there is posed a problem in that the gear, the parts thereof and the engaging claw may be broken due to the several hundreds of shocks generated by the collision of the gear and the engaging claw. For example, if it is assumed that the gear has five teeth, the pitch per one rotation of the gear is 1 mm and the thickness of the pipe is 20 mm, the engaging claw collides with the teeth of the gear five times while the pipe is cut by 1 mm. The engaging claw collides with the teeth of the gear one hundred times while the pipe is machined by 20 mm. If the cutting work is performed one hundred times per day, the collision will occur 10,000 times. If the cutting work is performed for one hundred days, the collision will occur 1,000,000 times. When the gear rotates at a high speed, the magnitude of shock grows larger, thereby adversely affecting the durability of the device.
In the device of prior art 1, cutting is performed only when the gear is caught by the engaging claw. It is therefore impossible to arbitrarily adjust the cutting depth. Thus, the range of choice of workpieces becomes narrow. That is to say, the cutting velocity and the cutting depth of a workpiece are determined depending on the material thereof or the kind of a tool used. In the prior art, there is a problem in that, even if such machining conditions exist, it is impossible to adjust the machining conditions.
The beveling angle of a pipe may vary depending on the kind and design of the pipe. The prior art has a disadvantage in that the beveling tool should necessarily be replaced in order to change the beveling angle.
In order to solve the aforementioned problem, technical studies have been conducted over a wide variety of fields. As a result, there has been developed a hydraulic control method which can easily transfer power, which can keep an input value and an output value substantially identical with each other and which is less susceptible to the centrifugal force of a rotary body.
As a related art of an orbital cutting device which hydraulically controls a cutting tool disposed within a rotary body, there is available a pipe severing device disclosed in Korean Utility Model Application Publication No. 1999-0012096 published on Apr. 6, 1999 (hereinafter referred to as prior art 2).
As shown in FIG. 8, prior art 2 is directed to a device which severs a round bar stock using the relative rotational movement between a round bar stock (P) which is a cut material and cutting tools (T1 and T2) which are cutting members. The device of prior art 2 includes: a cut material supply means (not shown) provided with a feed member for feeding a cut material by a predetermined length and a scroll chuck for firmly fixing the cut material; a cutting means provided with a cutting tool (T1) and a beveling tool (T2) and configured to be rotated at a high speed by a power transfer means so that the cutting means can cut a cut material while making relative rotation with respect to the cut material supply means; a power transfer means provided with a spindle drive pulley 74, a spindle 73 and a rotating plate 80 and configured to transfer rotational power to the cutting means; and an operation control means provided with a limit switch 90 and a plurality of hydraulic cylinders and beveling tool 32 control the operation of the cutting means. In the device of prior art 2, the cut material is kept stationary and the tools are relatively rotated to cut the cut material.
In the operation control means, a hydraulic fluid inlet port 72 is formed on a frame 71 installed in a fixing base 70. A pusher 75 disposed within the hydraulic fluid inlet port 72 is moved by the power of a hydraulic fluid supplied to the hydraulic fluid inlet port 72. The pusher 75 pushes two horizontal pushrods 81 disposed within the rotating plate 80 using a pusher flange 76 one-piece formed with the pusher 75. The pushrods 81 operate two vertical pistons 83 disposed within the rotating plate 80. By virtue of the operation of the vertical pistons 83, the cutting tool T1 and the beveling tool T2 are advanced and retreated in the direction perpendicular to the round bar stock P.
The limit switch 90 is connected to the pusher flange and is configured to detect the advanced state and retreated state of the pusher flange 76 for the utilization in automation.
Prior art 2 mentioned above has succeeded in allowing the external power to enter the rotary body. By detecting the application time of the external power, it is possible to realize automation of the device as a whole.
However, prior art 2 uses the external power only for the purpose of advance and automation of the cutting tool T1 and the beveling tool T2 and fails to use the external power in controlling the advance and retreat of the cutting tool T1 and the beveling tool T2. That is to say, the automation in prior art 2 is limited to an operation mode in which, after subjected to cutting and beveling, a round bar stock is moved into a machining position again. A problem is still posed in that it is impossible to accurately control the advance distance, the retreat distance and the re-advance of the tools.
Reviewing the detailed structure of prior art 2, the retreat of the cutting tool is performed by a spring 86 and the retreat of the pusher 75 is also performed by a spring 77. Accordingly, the cutting tool is not retreated by the external power but is retreated by the resilience force of the spring. This is mere return rather than control.
Furthermore, the vertical cylinder 83 and the pushrods 81 for moving the cutting tool are of a single-action type in which a hydraulic fluid flows into and out of a single port. This poses a problem in that the cutting tool is not rapidly advanced and retreated. More specifically, when the pressure is released in the hydraulic fluid inlet port 72 and the vertical cylinder 83 is moved upward by the resilience force of the spring 86, the hydraulic fluid flows through a single inlet/outlet port. Thus, the motion of the vertical cylinder 83 is slow. As a result, the advance and retreat of the cutting tool are not rapidly performed.
Prior art 2 is directed to a structure in which a roller 82 is used to rotatably connect the rotating pushrod 81 to the non-rotating push flange 76. In the structure employing the roller 82, the pushing force of the push flange 76 is transferred to the pushrod 81. However, the pulling force of the push flange 76 is not transferred to the pushrod 81. That is to say, even if the pressure is released from the hydraulic fluid inlet port 72 and the push flange 76 is retreated in order to control the retreat of the cutting tool, the pushrod 81 is slowly retreated by the resilience force of the spring 86 after the push flange 76 is moved away from the roller 82.
In view of the structural form of prior art 2 described above, there is a need to additionally innovate the structure of prior art 2 in order to accurately advance and retreat the cutting tool and to control the cutting tool in two or more axes so that the cross section of a round bar stock can be machined in many different shapes.